The present invention generally relates to the manufacture of cathode ray tubes and, in particular, to a method of cleaning the neck of a cathode ray tube.
The color cathode ray tube (CRT) typically includes an electron gun, a shadow mask, and a screen. The tube has a funnel shape, i.e., a wide opening that leads to a narrow neck. The electron gun is mounted in the neck of the tube and the screen is mounted proximate to the wide opening of the funnel of the tube. The shadow mask is interposed between the electron gun and the screen. A faceplate is sealed to the wide opening of the funnel. The screen is located on an inner surface of the faceplate of the CRT. The screen has an array of three different color-emitting phosphors (e.g., green, blue and red) formed thereon. The shadow mask functions to direct electron beams generated in the electron gun toward the appropriate color emitting phosphors on the screen of the CRT.
As part of the manufacturing process for a color CRT, the inside surface of the tube is coated with a conductive coating used to carry high voltage from a location on the side of the tube to the shadow mask. One method of applying the conductive coating is to use a flow coating process. The flow coating process comprises pouring the conductive coating material into the wide opening of the funnel and allowing the material to flow out along the funnel and through the neck of the tube. The material completely coats the funnel and neck. However, to create an operational CRT, the coating cannot extend along the entire neck of the tube. As such, it is necessary to clean the coating from a portion of the neck to a controlled dimension along the neck. The transition from the uncoated to coated portions of the neck must be uniform and the neck should be free of all contaminants.
Presently the process for cleaning the neck consists of inserting a multi-blade squeegee into the neck to a predefined distance along the neck. The squeegee is rotated to wipe the coating material from the inner surface of the neck. The problem with this system is that the squeegee wears during use and will ultimately leave streaks of coating material within the neck.
Therefore, there is a need in the art for a more effective method and apparatus for cleaning the neck of a color CRT.
A method of cleaning the neck of a funnel of a CRT during the manufacture thereof. The method comprises: inserting a drain tube within the neck, wherein the outer dimensions of the drain tube are less than the corresponding inner dimensions of the neck and a gap exists between the drain tube and the neck; directing a fluid through the gap; and draining the fluid that was directed through the gap, through the drain tube, whereby the fluid removes material and dirt from the neck.
The method utilized a cleaning apparatus, wherein the apparatus comprises: a cleaning unit having a housing that surrounds the neck; the drain tube that extends through the bottom of the housing into the neck to a predefined position within the neck which is below the top end of the housing; and a labyrinth flow controller positioned within the housing adjacent to the drain tube forming a laminar flow section whereby a flow of fluid is directed through the housing and along the interior of the neck and into the end of the drain tube.